Molecular and Genetic Mechanisms of Abnormal Cold Sensing – Implication for Thermoregulation, Obesity and Pain Research

皮肤中的冷痛感受器和温度感受器专门用来检测寒冷和有害的寒冷温度。它们的功能与体温动态平衡密切相关。尽管冷敏感皮肤神经末梢的分子专化性已被认识，但通过冷传导瞬时受体电位M8和A1通道，我们仍然对更复杂的生理功能知之甚少，例如导致冷低敏感和冷过敏的遗传和性别特异性机制。使用基于定制设计的温度梯度分析的大型筛选研究，我们在25个近交系小鼠品系中鉴定出在舒适温度选择上有性别差异和没有性别差异的冷低和冷过敏品系。对冷避避性状的品系和性别差异的遗传图谱分析使我们找到了在四个不同的系统中表达的候选基因，这些系统涉及体温调节和代谢：初级传入、下丘脑、肌肉和棕色脂肪组织。后者由于其在人体能量平衡调节中的关键作用，正日益引起肥胖研究的兴趣。除了在舒适温度选择和避寒方面的基本差异外，哺乳动物还通过各种调节手段对环境寒冷做出反应，从而延长了耐寒性，提高了舒适性，减少了能量消耗。到目前为止，这些冷适应机制的分子本质还没有被揭示，但我们的初步数据表明，TRPC5受体可能是一个很有希望的候选分子来介导冷适应，在有TRPC5的情况下，导致改善冷舒适，或者在没有TRPC5的情况下，通过调节初级传入冷敏感性来增加冷回避。TRPC5在三叉神经感觉系统中也有作用，我们的电生理数据表明，与TRPM8和TRPA1一起，TRPC5在牙齿中具有冷传导器的功能。缺乏三种冷传导器组合的转基因小鼠，加上最近开发的一项技术，允许我们通过小鼠牙槽神经-颌部准备记录牙髓伤害性感受器的传播动作电位，将为我们深入了解冷传导器在牙齿中的工作原理。此外，两个新的带有TRPA1和TRPC5荧光的小鼠品系与来自磨牙的逆行标记相结合，将使我们能够解决支配磨牙的正常神经和炎症神经以及三叉神经节中三个冷传导器的重叠。当寒冷变得痛苦时，除了核心体温保持外，生理功能是保护组织免受组织损伤和冻伤，但在神经病或神经损伤中，正常的寒冷被认为是灼痛。利用基于冷痛药理学模型的遗传作图方法，我们确定ADRA2b受体中的SNP是控制冷痛严重程度的潜在遗传因子，这一点将得到验证。

Cold nociceptors and thermoreceptors in the skin are dedicated to detect cold and noxious cold temperatures. Their function is tightly connected to body temperature homeostasis. Although the molecular specialization of the cold sensitive cutaneous nerve endings has been recognized, with the cold transducer Transient Receptor Potential M8 and A1 channels, we still have little knowledge about more complex physiological functions, for example the genetic and sex-specific mechanisms that lead to cold hypo- and hypersensitivity. Using a large screening study based on a custom-designed thermal gradient assay, we identified, among 25 inbred mouse strains, cold hypo- and cold hypersensitive strains and strains with and without sex difference in comfort temperature selection. Genetic mapping analysis of the strain and sex differences in the cold avoidance trait led us to candidate genes expressed in four different systems that are involved in thermoregulation and metabolism: primary afferents, hypothalamus, muscle and brown adipose tissue. The latter one, due to its critical role in body energy balance regulation, is becoming of increasing interest in obesity research. In addition to basic differences in comfort temperature selection and cold avoidance, mammals react to environmental cold by various means of adjustment leading to extended cold tolerance, improved comfort and decreased energy expenditure. So far, the molecular nature of these cold acclimation mechanism has not been revealed, but our preliminary data show that the TRPC5 receptor could be a promising candidate to mediate cold acclimation that leads, in presence of TRPC5, to improved cold comfort or, without TRPC5, to increased cold avoidance via adjustments of primary afferent cold sensitivity. TRPC5 has also a role in the trigeminal sensory system where our electrophysiological data imply a function as cold transducer in teeth together with TRPM8 and TRPA1. Transgenic mouse lines that lack combinations of the three cold transducers together with a recently developed technique that allows us to record propagated action potentials from tooth pulp nociceptors via mouse alveolar nerve-jaw preparations will provide us insight into how cold transduction works in teeth. Additionally, two new mouse lines with fluorescent TRPA1 and TRPC5 in combination with retrograde labeling from molar teeth will allow us to resolve the overlap of the three cold transducers in normal and inflamed nerves innervating molar teeth and in the trigeminal ganglia. When cold becomes painful, apart from core body temperature preservation, the physiological function is to protect from tissue damage and freeze injury, but in neuropathy or nerve injury, normal cold is perceived as burning pain. Using a genetic mapping approach based on a pharmacological model of cold allodynia, we identified a SNP in the Adra2b receptor as potential heritable factor that controls the severity of cold allodynia which will be validated.